CLOUD MODEL EXPERIMENTS OF THE EFFECT OF IRON AND COPPER ON TROPOSPHERIC OZONE UNDER MARINE AND CONTINENTAL CONDITIONS

We have used a multi-phase cloud photochemistry model to investigate the influence of dissolved iron (Fe) and copper (Cu) on the in-cloud production and loss of ozone and ozone-related species. Comparison of the results of our simulations with and without Fe and Cu reactions for three different photochemical scenarios (marine, averaged continental and polluted continental) indicate that Fe and Cu reactions, depending upon the scenario considered, can either increase or decrease the predicted rate of loss of ozone and ozone related species. For the marine and averaged continental scenarios the rate of loss of ozone in the aqueous-phase was decreased by as much as 45% and 70%, respectively, when Fe and Cu reactions were considered. For polluted continental conditions, the rate of loss of ozone in the aqueous phase increased with a factor 2 for low metal concentrations up to a factor 20 for high metal concentrations. In all three scenarios inclusion of the Fe and Cu reactions results in cloud droplets becoming more efficient sinks for gas-phase HO2 and also enhances OH production. The net effect of the decreased losses of ozone from the aqueous phase and the effect of the cloud droplets on HO2 and OH determine the overall impact on ozone and ozone related species, for each of the situations considered. Overall, when Fe and Cu reactions were included the marine cloud was found to be a less efficient sink for ozone, and averaged continental and polluted continental clouds were more efficient sinks for ozone (O-3 losses doubled in the averaged continental scenario). The higher OH flux in the aqueous phase also enhances the rate at which organic compounds, such as formaldehyde and formic acid, are oxidized in the cloud.